We really need a bit more information: HOW "doesn't (it) work as (you) expected?

1. Spew warnings; spit errors.... or what?
2. and what OS is this running under?
3. and HOW are you entering the input -- as a set of words on the CLI invoking the code, properly quoted; as individual words once the code is running; by telephathic instantiation?

See, among other FAQs about how to ask (and title) a question How do I post a question effectively? and I know what I mean. Why don't you?.

BTW, your code works as expected, when used to process input in the manner you've specified with <STDIN>... which is not the same way as it would work were you trying to process @ARGV.